The light radiation theory of light emitting diode (LED) is to generate light from the energy released by the electron moving between the n-type semiconductor and the p-type semiconductor. Because the light radiation theory of LED is different from the incandescent light which heats the filament, the LED is called a “cold” light source.
Moreover, the LED is more sustainable, longevous, light and handy, and less power consumption, therefore it is considered as a new light source for the illumination markets. The LED applies to various applications like the traffic signal, backlight module, street light, and medical instruments, and is gradually replacing the traditional lighting sources.